How large can an image go??

Hello all,
I'm getting ready to frame some of my photos. They need to be large though as they are for a retirement home (the elderly can't see all that well). I'm curious as to how i can tell just how large an image can go before it begins to get pixellation?

Something in photoshop perhaps?

I have a Digital Rebel XT if that makes a difference.

Thanks!

It's all image dependant.
At a bare minimum 200 ppi printing resolution, your camera can render a 11 x 17 print.
If you shoot RAW files, use near perfect field and digital darkroom techniques (tripod,non-destructive editing, etc.) and the highest quality lenses, then you should be able to make a larger print by letting Photoshop interpolate the image upward. How large depends upon the amount of detail present.

See this recent thread for some good info.

Again, it is going to be image dependant.

Try this as an experiment. Suppose you are considering printing an image at 30x45. Resize the file to that size. Next, crop out a section of it and print that piece to evaluate it. Ideally, you'll probably want to pull a good sized chunk out ot it such as 11x14 or 16x20, if your printer will allow for it. There is a danger that if you print an 8x10 crop of the resized image, you'll look at it nose close rather than standing back a bit like you would for a larger print.

You may also find that the image may require some experimentation on resizing and sharpening.

As the others said, its image and size dependent. I've printed images captured with the same camera as large as 20x30 - never gone larger but at that size some look great to my eye, others look horrid to my eye (I should say all looked great from a descent distance ;) ). I'd recommend a bit of experimentation with crops that Dan suggested, experimenting with interpolation (enlargement) and sharpening in these test prints.

Thanks guys...I'll play around with it today if I have time.

It doesn't just depend on the Camera it more depends on the lens I would say. If you were to take overlapping shots and stitch them together you can always go a lot bigger. Just my 2 cents!

Like you said, elderly people don't have quite the vision that their younger counterparts do, so you could probably print larger for them than you would others and get away with it. And if anyone questions it, just tell them they need to have their eyes tested!

Probably large enough for any reasonable person, if you do everything right. I'm sitting in front of a 24x36 inch print made from a digital capture with a 6 mp Fuji S2 pro. This is a photograph of an immobile subject (rock art) taken with an immobile camera (sturdy tripod, cable release, highly skilled amateur photographer, etc.) at low ISO. The print looks quite fine because I always view it from at least four feet away! If you look at my NPN photographers gallery image I am holding that print...before it was framed (it isn't as pink as it looks there, and that clock still says 10:15, and a grew the beard back after a year without!).

I've made a few 20X30 prints from my XT. They look good, but they don't hold up to close inspection the way that large format shots do.